1. Field of the Invention
The present invention relates to a three-dimensional measurement device, and more particularly, to an improvement in a three-dimensional measurement device for extracting a geometric element from a point cloud representing a three-dimensional shape of a measurement target object and displaying a distribution of deviations.
2. Description of Related Art
A three-dimensional measurement device is a measurement instrument for three-dimensionally measuring the shape or the dimensions of a measurement target object, and is capable of acquiring three-dimensional shape data containing position information of a large number of measurement points in a three-dimensional space. The acquired three-dimensional shape data is displayed as a three-dimensional shape obtained by three-dimensionally arranging the large number of measurement points, for example. In dimension measurement, the distance or the angle between geometric elements is determined by extracting a plurality of geometric elements. A geometric element at a measurement position may be extracted by designating the type of a basic shape, and selecting a point cloud consisting of a plurality of measurement points.
Furthermore, by determining a deviation from a geometric element for each measurement point included in a point cloud, and superimposing and displaying, on a three-dimensional shape, a distribution of deviations from the geometric element, undulation of a surface of a measurement target object or dispersion of measurement points may be visualized.
With a conventional three-dimensional measurement device as described above, only the deviation distribution regarding a single geometric element, among geometric elements extracted from a point cloud, can be displayed. Accordingly, it is difficult to compare the degree of undulation for a plurality of geometric elements of a three-dimensional shape. Also, only the deviation distribution from a plane can be displayed.
FIGS. 15A to 15C are diagrams showing an operation of a conventional three-dimensional measurement device. FIG. 15A shows a three-dimensional shape of a measurement target object W displayed on a screen. The measurement target object W has stair-like steps, and it is conceivable to examine the degree of undulation for two surfaces of an upper surface S1 of the lower step and an upper surface S2 of an upper step. In this case, first, a point cloud is selected on the three-dimensional shape being displayed, and a geometric element is extracted.
FIG. 15B shows a deviation distribution which was determined with the upper surface S1 of the lower step as a reference surface. One geometric element corresponding to the upper surface S1 is designated as a reference surface, and deviations of measurement points from the reference surface are determined. A deviation distribution determined in this manner may be superimposed and displayed on the three-dimensional shape. For example, different colors are assigned to respective measurement points according to the deviations. FIG. 15C shows a deviation distribution which was determined with the upper surface S2 of the upper step as a reference surface. When a geometric element corresponding to the upper surface S2 is designated as a reference surface, a deviation distribution for the reference surface is superimposed and displayed on the three-dimensional shape.
As described above, according to a conventional three-dimensional measurement device, only one geometric element can be designated as the reference surface for determining the deviation. Also, as shown in FIG. 15B, at a part D1 above the upper surface S1, a deviation upper limit for color assignment is exceeded, and the part is assigned with a single display color (red), and at a part D2 below the upper surface S1, a deviation lower limit for color assignment is not reached, and the part is assigned with a single display color (blue). According to such display of deviation distribution, because parts other than the upper surface S1 are solidly colored, the three-dimensional shape of the measurement target object W cannot be recognized.